diff --git a/education/software development/ECE1400/Chapter 15 Exercises.md b/education/software development/ECE1400/Chapter 15 Exercises.md
index 0d56933..90c787c 100644
--- a/education/software development/ECE1400/Chapter 15 Exercises.md	
+++ b/education/software development/ECE1400/Chapter 15 Exercises.md	
@@ -59,7 +59,8 @@ main.o: main.c f1.h
 f1.o: f1.c f1.h
 	gcc -c f1.c
 
-f2.o 
+f2.o: f1.o f2.c f2.h
+	gcc -c f2.c f1.o
 
 ```
 ---
@@ -67,8 +68,12 @@ f2.o
 > **6.** The following questions refer to the program described in Exercise 5.
 > (a). Which files need to be compiled when the program is built for the first time?
 
+`f1.c`, `f1.h`, `f2.c`, `f2.h`, `main.c`, `main.h`
+
 > (b). If `f1.c` is changed after the program has been built, which files need to be recompiled?
 
+All dependents of `f1.c` and `f1.c`, in this case `f1.c`, `main.c`, and `f2.c` (including header files).
+
 > (c). If `f1.h` is changed after the program has been built, which files need to be recompiled?
 
 > (d). If `f2.h` is changed after the program has been built, which files need to be recompiled?